Processes which include condensation of one or more carbonyl-containing reactants to form an unsaturated carbonyl-containing compound, and hydrogenation of said unsaturated compound to a saturated carbonyl-containing product, are well known.
One such process is the preparation of methyl isobutyl ketone (MIBK) from acetone. In this process condensation of two acetone molecules yield diacetone alcohol (DAA) which is dehydrated to yield mesityl oxide (MSO), and the MSO is hydrogenated to MIBK. The condensation and dehydration reaction takes place in the presence of an acidic catalyst, and the hydrogenation takes place in the presence of a hydrogenation catalyst such as a noble metal.
The production of MIBK can take place in two process steps as indicated above or in a single process step in the presence of a single condensation and hydrogenation catalyst. Such single step processes are disclosed in, for example, U.S. Pat. No. 3,574,763; EP 1 32 1 450 and South African complete patent application number 2004/8988.
The MIBK produced from the condensation and hydrogenation of acetone includes one or more impurities such as propane, isobutane, methyl pentane, acetone, 2-propanol, water, diacetone alcohol (DAA), mesityl oxide (MSO) and high boiling compounds such as diisobutyl ketone, C9 paraffins and ketones.
Methods of purifying MIBK are also known in the art. The article “Why not do it in one step”, Chemtech, January 1977 discloses a process wherein the MIBK reaction products are subjected to a gas separator to remove unreacted hydrogen for recycle to the MIBK reactor. The liquid from the gas separator is fed to a first distillation column where acetone is recovered as an overhead product and recycled to the MIBK reactor. The bottom product of the first column is then fed to a liquid-liquid separator (decanter), where the aqueous phase is removed from the process and the organic phase is fed to a second distillation column somewhere between the take-off of the bottom product and a reflux entry position. An overhead low boiling product is removed as distillate in the second column. The bottom product of the second column is then fed to a third distillation column where high boiling compounds are removed as the bottom product and MIBK is removed as the distillate.
“Methyl Isobutyl Ketone by Direct Condensation of Acetone”, SRI Reports, May 1972, discloses a similar process as described above. The main difference is that the first distillation column described above is replaced by two columns, namely a first distillation column where low boiling products (particularly methyl pentane as an azeotrope with acetone) are removed as a distillate. The bottom product is then fed to a second column where the unreacted acetone is removed as a distillate and recycled to the MIBK reactor. Another difference is that the third column (similar function as the second column above) is fitted with an overheads decanter.